Transmissions receive an input rotational torque and rotational speed from an input device coupled to a power source (e.g., an input shaft), convert the rotational torque and speed received from the input device, and transmit the converted rotational torque and rotational speed to an output device (e.g., output shaft). For instance, in some applications transmissions convert or adjust the rotational speed received from the input device such that the rotational speed of the output device varies from the rotational speed of the input device, and where the ratio of the rotational speeds of the input and output devices defines a speed or gear ratio of the transmission. Transmissions are used in a variety of applications, including motor vehicles, construction machinery, power generation systems, and other industrial machinery.
In some applications, transmissions comprise a plurality of discrete and selectable gear ratios between the input and output devices. In these applications, the desired gear ratio of the transmission may be selected manually in manual transmissions and automatically in automatic transmissions. In other applications, transmissions are configured to change seamlessly through a continuous range of gear ratios, such as continuously variable transmissions (CVTs). In certain applications, CVTs are configured to allow the input shaft to remain at a constant rotational speed while continuously varying the rotational speed of the output device, allowing the power source coupled to the input device to operate at a preferred rotational speed, such as the rotational speed that provides optimum power or fuel efficiency.
In some applications, CVTs may comprise a belt or chain frictionally engaging a pair of rotatable pulleys, where each pulley includes a continuously adjustable outer diameter to vary the gear ratio between the rotatable pulleys. Given that these CVTs rely on frictional engagement between the belt and the pulley, instead of engagement between interlocking gear teeth in traditional automatic and manual transmissions, some CVTs may be limited in the amount of torque they may transmit between the input and output devices. Further, other CVT designs may include a relatively large number of moving parts, limiting their durability and increasing the effort and cost to design, manufacture, maintain, and repair.